Improve the Processor base class and SanitizePasswordsProcessor class

Improve Processor to also check for stacktrace at the 'data' level.  A stacktrace can exist in the data
even without an 'exception' key.
Also added 'pw' and 'cred' to the list of FIELDS to screen for in SanitizePasswordProcessor.  These
two fields being used in the standard python LDAP module.
Do we have a test that highlight why this is needed ?